Why you need to ditch the diet if you want to lose weight

Tim Spector, a physician and professor of genetic epidemiology at King's College London, wants to debunk healthy-eating mantras. Spector decided to rethink his eating habits after a skiing accident left him with high blood pressure, and to investigate the role played by gut microbes in maintaining our health. He draws on his research on microbes, genetics and diet to explore our relationship with food, and to investigate how we can nurture a healthy microbiome1 by eating according to science.

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WIRED: In your book The Diet Myth, you refer to the "myth of modern diets". What is this?Tim Spector: There are many myths: the first one states that if everybody follows the same calorie control and does some exercise, then they will lose weight. Another myth states that by restricting and reducing certain items you will lose weight and be healthy. This is the trend of fad diets where people pick on one group of food and avoid others – whether that be gluten, grains, dairy, fat or meat – at all costs. Another fallacy is that grazing rather than gorging is better to maintain our blood glucose levels, and help us lose weight.

Why are myths around food so toxic for our health?If people have followed advice in the past 30 years, they would have mainly followed low-fat diets – switching from butter to margarine, avoiding nuts and high-fat dairy products like cheese and either selecting low-fat yoghurts or avoiding them completely. The whole idea limits the range of foods that people consume, so that not only do we eat an unbalanced diet with no real nutrition but it is much lower in fibre now than it was 30 or 40 years ago.

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The artificial sweeteners inside processed foods – which we thought were harmless – also induce our microbes to produce inflammatory and metabolic chemicals that make you more likely to put on weight or get diabetes. It's the double whammy of all the chemicals in these processed foods, plus the lack of fibre that hit our gut microbes hard.

How much do we know about the role microbes play?We can't live without microbes – they are crucial for the development of our brain and our immune and digestive system. There are an estimated one hundred trillion microbes in our guts. They produce a third of our vitamins and minerals as well as brain chemicals such as serotonin, which are responsible for our mood. If we wipe out our gut microbes then our immune system goes into auto-drive and starts attacking us with autoimmune diseases and allergies. Over millions of years, we've slowly incorporated microbes and worked as a team. In the past few decades, we've been trying to wipe them out – without knowing what we are doing – and this is causing us problems.

What foods should we consume – and why – to maintain a healthy microbiome?Everybody has a different set of microbes – like a unique microbial fingerprint. At present, we don't know how to personalise in order to help our own microbes. Our studies have shown that you can make animals sick by reducing the diversity of their microbes. So you need to have a diet that increases the diversity of your microbes: that involves avoiding antibiotics, pesticides and chemicals in food and increases your fibre intake as well as its diversity, because for each little change in fruit or vegetable, you've got a whole community of different microbes that will feed off it.

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Nuts, seeds, dark chocolate, red wine, olive oil and vegetables like leeks, onions, garlic and artichokes are really packed with chemicals that microbes love. This is probably why the Mediterranean diet is the only one that has proven to be beneficial for health. We also need to be regularly consuming more fermented foods such as live yoghurt, kefir, sauerkraut or kimchi as a source of natural microbes.

Which principles are backed up by scientific evidence?I favour ones that don't interfere with the diversity of what you're eating. So how can you lose weight while keeping your gut microbes healthy? The only diet that does that is intermittent fasting. You can maintain the same things that you eat, but intermittently change the total amount so that a few days out of seven you're consuming only 500 calories. That's the diet that most people stick to – 80 per cent of those who took part in a six-month trial maintained it.

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To what extent do our genetics influence our relationship with the foods that we consume?I used to think that our food choices were driven by what our parents fed us, or the general environment that you were in. So if you came from southern Europe you'd be more likely to like garlic – because you're surrounded by it – than if you live in northern Europe. It turns out that I was wrong: preferences for many of the bitter-tasting foods such as broccoli, sprouts and garlic are genetically determined. Nearly all the things we looked at in our study on twins2 had a genetic influence as well as a cultural one. There's even a genetic basis for how much you like junk food. Some of this may be related to our very different gut microbes.

What are you researching next?I'm interested in identifying the specific microbes that are associated with various diseases, and then working out what foods we need to tailor our diet and improve these microbes and self-medicate with them.

1. The microbiome refers to the trillions of microbes and other bacteria that live inside our bodies.

2. In 2014, Spector published a study in Cell Press comparing the microbiotas across over 1,000 fecal samples obtained from 416 pairs of twins.

This article was first published in the June 2016 issue of WIRED magazine